1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays and other devices involving fine structures. In a conventional lithographic apparatus, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device). This pattern can be imaged onto a target portion (e.g., part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning device may comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (e.g., the “scanning” direction), while synchronously scanning the substrate parallel or anti parallel to this direction.
The individually controllable elements that generate the pattern in the patterning device may take several forms. Conventionally, there are two types of pure-phase modulating individually controllable elements. A first type is based on a reflective layer placed on a compliant layer. A second type is based on individual micro-mirrors that can be moved in a direction perpendicular to their reflecting surface.
However, both of these types of individually controllable elements are difficult to manufacture and are not efficient in accurate pattern placement when trying to also maintain pattern fidelity. This is largely because of they require mechanical motion for arrays of very small individually controllable elements.
Therefore, what is needed is a system and method that can provide a pure phase-shifting array of individually controllable elements that is capable of accurate edge placement without loss of pattern fidelity.